Re: [STDS-802-16-MOBILE] Length of RS-CC code blocks
Patrick
In OFDM mode, the span of the FEC and interleaver are as follows:
1. An interleaver block is the equivalent of an OFDM symbol.
2. The RS code, (which is applied only in the non-subchannelized case) spans
the equivalent of one OFDM symbol. Note that in subchannelized mode RS is
bypassed.
3. The CC code spans the entire burst. A zero tail byte is appended at the
end of the burst.
I have not verified the example provided, and I cannot address your remark
on the strange pad bits. However the parameters of the example (8.3.3.5.3)
were chosen to demonstrate a specific anomaly in which the number of data
bits is not an integer number of bytes.
In a single subchannel, in QPSK 3/4, there are 18 data bits per symbol. The
10 data bytes and the 1 tail byte are equivalent to 88 bits of data which
are carried in ceil(88/18)=5 OFDM symbols. Thus 5*18-88=2 additional pad
bits are required. This is as described in (8.3.3.2.1 pp 433 line 55) " When
the total number of data bits in a burst is not an integer number of bytes,
zero pad bits are added after the zero tail bits".
Hope this helps
Tal
-----Original Message-----
From: Patrick Fuller [mailto:patrickf@PICOCHIP.COM]
Sent: Friday, June 11, 2004 10:04 AM
To: STDS-802-16-MOBILE@listserv.ieee.org
Subject: [STDS-802-16-MOBILE] Length of RS-CC code blocks
I have a basic question to do with how many symbols a RS-CC FEC code
block can be spread across for OFDM-256. By my interpretation of the
spec, things are simple for the non-subchannelization case: you get one
RS-CC code block per symbol. However, for the subchannelization case, I
find the spec somewhat contradictory:
- There is a sentence at the end of 8.3.3.2.1 (the RS-CC section) that I
interpret as meaning each that each allocation's RS-CC code blocks are
spread across just one symbol (just like the non-subchannelization
case): "The Uncoded Block Size and Coded Block size may be computed by
multiplying the values listed in Table 213 by the number of allocated
subchannels divided by 16."
- However, the "Example OFDM uplink RS-CC encoding" (8.3.3.5) seems to
contradict this. 8.3.3.5.2 ("Subchannelization (2 subchannels)") shows
an example where a single RS-CC code block is spread over 3 symbols.
8.3.3.5.3 ("Subchannelization (1 subchannel)") gives an example where
the RS-CC code block is spread over 5 symbols. (Further, there are some
"strange" extra padding zero bits/bytes this example, not mentioned
earlier in the proper spec.)
I'd be very grateful to hear any views on this.
Thanks,
Patrick Fuller
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